1. Field of the Invention
The present invention generally relates to a power distribution system, and more particularly to a power line layout.
2. Description of the Prior Art
A structure commonly referred to as the metal power line is one of the important elements in the power distribution system of a chip, a printed circuit board, or a package. The power line provides a path or way for transferring a supplied power, such as VDD, to a variety of circuits or electronic components in an entire electronic system. FIG. 1 schematically shows a conventional power line 10 that consists of a rectangular plane metal wire laid out on a substrate 12, while other circuits or electronic components are left out in the figure. The power supply (not shown in the figure) typically supplies the power at both ends (A and B) of the power line 10.
FIG. 2 shows an equivalent schematic of the power line 10 that consists of series-connected resistors R (e.g., with four representative resistors R being shown in the figure). Current sources I respectively represent current drawn away from the interconnecting nodes of the resistors R by other circuits or electronic components (not shown).
According to the equivalent schematic of FIG. 2, the IR drop at or near either end (A or B) has a greater rate of change than the middle node (M) as a consequence of the supplied current at either end (A or B) being greater than that at the middle node M. FIG. 3 shows an exemplary relationship curve between the IR (current times resistance) voltage drop and the distance traveled along the power line 10. According to the figure, the curve has a slope that is greater at or near either end than at the middle.
As the number of electronic components (such as transistors) has been increasing and the operating voltage of the electronic components has been decreasing in modern integrated circuits, the IR drop more substantially affects the operation of the electronic components, or even causes the circuits to malfunction.
For the reason of a conventional power line having a substantive IR drop problem, particularly at the ends of the power line, a need has arisen to propose a novel power distribution system that can improve or eliminate this IR drop effect.